Design
| Enviro |
Astro | Propulsion
| Power | Thermal
| Structures | AD&C
| CDHS |
Test
These
are rapidly emerging propulsion methods
that
offer very high specific impulse, Isp.
Electric
Propulsion
Electrostatic
ion thrusters ionize a fluid (xenon, mercury, rubidium,
potassium or cesium) with an electric discharge.
An electrostatic field accelerates this ion propellant
to produce thrust. Electrons are injected into the
exhaust to neutralize ions and prevent spacecraft
charging. Xenon is the most widely used fluid. It
is a safe and inert gas with favorable storage characteristics
for spacecraft. Isp may
reach up to 10,000 seconds, which indicates a very
efficient engine. The NASA/Caltech JPL DS1
spacecraft was the first to successfully demonstrate
this revolutionary technology.
Electromagnetic
propulsion uses an electric
arc or electromagnetic field to accelerate positive
ions in a plasma. Hall-effect thrusters (HET) apply
a radial magnetic field to plasma that accelerates
the positive ions. Russia has developed advanced
HET systems for station-keeping with Isp values
around 2000 seconds. Teflon pulsed-plasma thrusters
(PPT) expose solid Teflon propellant
to high voltage arcs. It vaporizes
into a plasma, which is then accelerated by the
associated induced magnetic field. Teflon PPT systems
have long lives and are used for station keeping.
Isp varies from 700 to 1500 seconds.
